This application is based on application No. RM2001 A 000048 filed in Italy, the content of which is incorporated hereinto by reference.
The present invention relates to a method of preparing physiologically acceptable aqueous solutions and water-soluble compositions suitable for obtaining them, as well as the solutions and the compositions thus obtained.
More particularly, the present invention relates to physiologically acceptable aqueous solutions and water-soluble compositions suitable for obtaining them, comprising a first physiologically acceptable compound of an acidic nature, a second physiologically acceptable compound of a basic nature and a trisubstituted salt of glycyrrhizic acid.
In therapeutic and cosmetic practice, both human and veterinary, use is often made of aqueous solutions containing a carboxylic acid or an organic base, possessing low intrinsic solubility (solubility of the undissociated compound). Their salification (generally with alkali metals or hydrophilic amines of low molecular weight for the acids, and with hydrogen halides or hydrophilic organic acids of low molecular weight, for the bases) is employed to provide them with adequate solubility.
Sometimes it is useful to have aqueous solutions containing at least one carboxylic acid and at least one organic base at the same time. Since solutions with basic pH are needed for the solubilization of weak organic acids, and solutions with acid pH are needed for the solubilization of weak organic bases, such compounds often display a high degree of incompatibility in ordinary aqueous solutions because mutual precipitation occurs on mixing them (see A. T. Florence and D. Attwood xe2x80x9cPhysiochemical Principles of Pharmacyxe2x80x9d, II edition, Portland Oreg., 1988, p. 154).
Examples of this behaviour that are well known in the literature are the solutions of acetylsalicylic acid (lysine salt) with chlorpromazine (hydrochloride) or promethazine (hydrochloride) (Repertorio Farmaceutico Italiano 1989 (REFI) page A-578); solutions of furosemide (sodium salt) with organic bases (REFI, page A-808); solutions of dimemorfan (phosphate) with penicillin (sodium salt) or of sodium salicylate (REFI page A-646).
It should be noted, moreover, that the phenomenon is rather more complex than might appear at first sight because, depending on circumstances, there may be precipitation of the acid compound, or of the basic compound, or of a mixture of the two, or of adducts, known as hydrophobic ion pairs. In this last case, which is very common, there may be formation of precipitates, even when one of the two components, for example quaternary ammonium compounds, has good intrinsic solubility.
The incompatibility is more or less pronounced depending on the pK, on the nature and on the intrinsic solubility of the components that determine it. In fact, cases of absolute incompatibility are encountered in practice, in which it is practically impossible to obtain solutions containing the two pharmacologically active compounds at any therapeutically useful concentration, and cases of partial incompatibility in which it is possible to obtain solutions but only in a very restricted range of concentration.
The problem of incompatibility is not solved by separate administration of the solutions of the different pharmacologically active compounds to the patient, unless there is a considerable interval of space and/or time between the applications. Otherwise, in fact, incompatibility between the two pharmacologically active compounds and inactivation occur at the site of actual application (see, for example, the case of cephalosporins and of aminoglycosides (REFI page A-249)). In each case separate application, besides being inconvenient, proves completely impossible in some cases, for example when one of the compounds performs the functions of a preservative.
In some cases the problem has been solved by using specific pharmaceutical formulations. Thus, the incompatibility between certain carboxylic acids and certain basic decongestants is eliminated by means of a mixture of polysorbates and a polyoxamer (U.S. Pat. No. 5,459,157). Moreover, it should be pointed out that in this case, as in other similar cases, the concentration of these additives is very high (12%) relative to that of the pharmacologically active compounds (0.05-0.1%).
Glycyrrhizic acid, the principal component of the extract of Glycyrrhiza Glabra, was isolated by Karrer and Chao and its tricarboxylic acid structure was established by Ruzicka in 1943 (Merck Index, XII ed., 4515). Two epimers of glycyrrhizic acid are known, designated 18xcex1 and 18xcex2, but the second is the commonest and it is this that is being referred to whenever the nature of the epimer is not expressly indicated (Runti, Fondamenti di chimica farmaceutica [Fundamentals of pharmaceutical chemistry], Trieste 1969, Vol. III, page 265).
Various salts of glycyrrhizic acid, called glycyrrhizinates, have been described in the literature.
A typical, commercially available monosubstituted salt is the monoammonium salt xe2x80x9cGlycamil(trademark)xe2x80x9d of the company Indena of Milan. Typical disubstituted salts are the dipotassium salt, xe2x80x9cRitamectant K2(trademark)xe2x80x9d of the R.I.T.A. Corporation, and the mixed salts of potassium, calcium and magnesium called xe2x80x9cglycyrrhizinesxe2x80x9d (U.S. Pat. No. 4,176,228). A typical trisubstituted salt is the tripotassium salt (Voss et al., Ber. 70, 122, 1937).
The monosubstituted and disubstituted salts are widely used in the food and pharmaceutical industry, principally as sweeteners.
Apart from some mild therapeutic activities that have been under investigation for several years (antiulcer activity, anti-AIDS activity, treatment of hepatitis B), certain functions of glycyrrhizic acid and its salts as xe2x80x9cadjuvantsxe2x80x9d in pharmaceutical formulations have also been described from time to time.
The action of xe2x80x9cenhancersxe2x80x9d of absorption through the skin and the mucous membranes is well documented (U.S. Pat. Nos. 5,183,802; 5,238,917; JP 3099023).
Japanese patent JP 10025255 proposes the use of glycyrrhizic acid, its salts or its esters, for the preparation of solid complexes with antiulcer, anti-inflammatory or antihistaminic drugs for the purpose of improving their absorption (rate of solution). It is known, however, that the complexes that can be used for increasing the rate of solution cannot be used for increasing equilibrium solubility (A. J. Repta in xe2x80x9cTechnique of Solubilation of Drugsxe2x80x9d (S. H. Yalkowsky ed. Marcel Dekker N.Y. 1981 page 135 ff.; pages 149 and 151).
In two Japanese patent documents (Jpn Kokai 0283,318 and JP 3145432A) reference is made to clear solutions containing salts of glycyrrhizic acid, quaternary ammonium compounds and respectively, sodium condoitrinsulphate, borax and taurine in the first case, and lysozime (hydrochloride) in the second. In the first case (C.A. 113, 65296x) the salt used is dipotassium glycyrrhizinate.
U.S. Pat. No. 4,481,187 discloses the use of glycyrrhizic acid or its salts for solubilizing oily substances in water, such as oil-soluble hormones and perfumes.
JP 09 087201 discloses a liquid composition containing acetaminophenone, a saccaride, a salt of glycyrrhizic acid and a glycol. Acetaminophenone, however, is neither acid nor basic in nature. Indeed, it is neutral.
In patents relating to the use of glycyrrhizic acid, generally reference is made to its salts, without differentiating them. However, monosubstituted and disubstituted salts are normally used in the examples given in these documents. Just occasionally, as in U.S. Pat. No. 4,278,657, which proposes the use of glycyrrhizic acid and its salts in synergy with certain polysaccharides as emulsifiers of water and oil mixtures, examples with trisubstituted salts are also given. However, neither this nor other patents describe or claim that the trisubstituted salts have any property at all that is different from the mono- and disubstituted salts.
It has now been found, unexpectedly, that the compositions comprising the salt of a first physiologically acceptable compound of an acidic nature and the salt of a second physiologically acceptable compound of a basic nature, which give rise to mutual precipitation in water, can easily be solubilized in water by adding a suitable amount of a trisubstituted salt of glycyrrhizic acid. Naturally, apart from a first physiologically acceptable compound of an acidic nature and a second physiologically acceptable compound of a basic nature, other physiologically acceptable compounds of an acidic and/or basic nature can also be present.
In a first aspect, the present invention therefore relates to a method for forming an aqueous solution comprising a first physiologically acceptable compound of an acidic nature and a second physiologically acceptable compound of a basic nature that are able to give rise to a precipitate in water, characterized in that a trisubstituted salt of glycyrrhizic acid is added in sufficient quantity to form a clear solution.
In a second aspect, the present invention relates to a physiologically acceptable aqueous solution comprising a first physiologically acceptable compound of an acidic nature and a second physiologically acceptable compound of a basic nature that are able to give rise to a precipitate in water, characterized in that it also includes a trisubstituted salt of glycyrrhizic acid in sufficient quantity to form a clear solution.
Moreover, in a further aspect, the present invention relates to a composition comprising a first physiologically acceptable compound of an acidic nature and a second physiologically acceptable compound of a basic nature that are able to give rise to a precipitate in water, characterized in that it also includes a trisubstituted salt of glycyrrhizic acid in sufficient quantity to form a clear solution when the said composition is added to water.
For the purposes of the present invention, the glycyrrhizic acid can be either in the form of epimer 18xcex1 or of epimer 18xcex2. The latter is preferred, however, because it is more readily available commercially.
The cation of the trisubstituted salt of glycyrrhizic acid according to the present invention can be any physiologically acceptable, organic or inorganic cation, for example sodium, potassium, ammonium, calcium, magnesium, monoethanolamine, diethanolamine, triethanolamine, lysine, arginine, tromethamine and the like. There is no limitation on the use of mixed trisubstituted salts.
Solutions of disodium monoammonium glycyrrhizinate obtained by neutralizing the commercial ammonium monoglycyrrhizinate with the required quantity of aqueous solution of sodium hydroxide are easily accessible and particularly advantageous. For example, with a 0.2 N solution of sodium hydroxide it is easy to obtain a solution of disodium monoammonium glycyrrhizinate at concentrations above 8%, the exact value depending on the strength of the commercial ammonium glycyrrhizinate used. Naturally, neutralization can also be carried out, as well as with sodium hydroxide, with potassium hydroxide, with ethanolamine, with diethanolamine, with ammonia or with their obvious equivalents.
Because the absolute concentration and the proportions between the components in the composition of the invention are not determined by stoichiometric requirements but by therapeutic or pharmaceutical requirements and because the phenomenon of mutual precipitation is governed by the nature of the components, there is not an optimum concentration of trisubstituted glycyrrhizinate that can be used in all cases.
However, it is very easy to identify it in any individual instance by mixing together, with vigorous stirring in water, a salt of a first physiologically acceptable compound of an acidic nature and a neutral salt of a second physiologically acceptable compound of a basic nature that are able to give rise to a precipitate in water, at the concentration and in the proportions that are predetermined by therapeutic, pharmaceutical, cosmetic or similar requirements. Then an aqueous solution of a trisubstituted glycyrrhizinate is added gradually, in portions, to the suspension that forms, until a clear solution is obtained. Preferably, the total amount of water is preselected so that at the end of the operation the total volume is reasonably lower (5-10%) than the required final volume and then it is made up to volume with water. Advantageously, the aqueous solution of glycyrrhizinate is added very slowly and with vigorous stirring. In fact, attainment of equilibrium in a few hours is by no means rare.
The amount of trisubstituted glycyrrhizinate required to achieve solubilization of the precipitates varies, in the examples given further on, between 0.27 and 2.7% (concentrations expressed as disodium ammonium glycyrrhizinate). However, for the reasons previously presented concerning the nature of the phenomena involved and the factors affecting them, a person skilled in the art will easily understand that the amount of trisubstituted glycyrrhizinate required could, in a particular case, also undergo reasonable deviations, higher or lower relative to the aforesaid range, while remaining within the scope of the present invention.
Having thus easily determined in the laboratory the appropriate quantity of trisubstituted glycyrrhizinate required for the particular composition under consideration, large-scale preparation of the solutions of the invention will preferably be effected by mixing together, in the desired order, the predetermined quantities of the various components as solids or as solutions.
For example, the following are added, in this order, to a preselected quantity of water:
a quantity of a base (for example sodium hydroxide, potassium hydroxide, ethanolamine, diethanolamine, triethanolamine, tromethamine, lysine, arginine, or sodium bicarbonate) sufficient to salify either the two free carboxyls of the predetermined quantity of ammonium glycyrrhizinate, or the preselected quantity of a physiologically acceptable compound of an acidic nature if the latter is used as free acid as well as salt;
the said physiologically acceptable compound of an acidic nature
the monoammonium glycyrrhizinate, and
the preselected quantity of a neutral salt of a physiologically acceptable base.
If the salt of the physiologically acceptable base is an acid salt, for example the sulphate or those of dicarboxylic acids, due account of it is taken by suitably increasing the initial quantity of base. Similarly, the quantity of base used will be reduced whenever the physiologically acceptable base is used in the free form as well as in the form of salt.
So far, no appreciable drawback has been observed when using an excess of trisubstituted glycyrrhizinate, relative to the minimum quantity required for obtaining a clear solution. Indeed, an improvement in stability of the solution has been observed in some cases.
The compositions of the invention could also be in the form of powders for dissolving or as concentrated solutions for diluting in water, or in aqueous liquids, at the time of use. Forms that could be used for this purpose are granules, freeze-dried products, tablets and the like, produced by traditional galenical techniques, well known to a person skilled in the art, comprising simple operations such as granulation, tableting, dissolving, sterilizing, freeze-drying etc.
Preferably, the physiologically acceptable compound of an acidic nature according to the present invention is a carboxylic acid.
In its turn, the physiologically acceptable compound of a basic nature according to the present invention is, preferably, an organic base.
The physiologically acceptable compounds that are preferred according to the present invention are those that display a therapeutically useful pharmacological or pharmaceutical activity.
The physiologically acceptable compounds of an acidic nature, characterized in that the aqueous solutions of their salts (with alkali metals and alkaline earth metals, ammonium, hydroxyamines, basic amino acids, tromethamine etc.) are incompatible with aqueous solutions of salts of organic bases, and belong to various chemical therapeutic categories.
A typical example of a first important class of these compounds comprises the non-steroidal anti-inflammatory drugs (NSAIDs). Typical examples of NSAIDs are arylalkanoic acids (ketoprofen, napoxen, ibuprofen, flurbiprofen, diclofenac, sulindac and the like), anthranilic acids (mefenamic acid, flufenamic acid and the like), salicylic acids (aspirin, diflunisal and the like), and some heterocyclic acids (indometacin, flunoxaprofen, ketorolac).
A typical example of a second class comprises diuretics such as ethacrynic acid, furosemide and the like.
A typical example of a third class comprises anti-allergic drugs such as lodoxamide, tranilast and their analogues.
A typical example of a fourth class comprises the 21-phosphoric and 21-hemisuccinic esters of corticosteroids.
Further examples of therapeutically useful compounds of an acidic nature characterized by the fact that aqueous solutions of their salts are incompatible with aqueous solutions of salts of organic bases are carboxylic acids belonging to other therapeutic classes such as: aryloxy-alkanoic acids, sorbic acid, pirfenoxone, folic acid, fusidic acid, theophylline-acetic acid, bendazac, prostaglandins, ACE inhibitors, penicillins, cephalosporins, quinolonics and the like.
The physiologically acceptable compounds of a basic nature, characterized in that the aqueous solutions of their salts (with hydrogen halides, sulphuric acid, phosphoric acid, nitric acid, low molecular weight organic acids, hydroxylates and/or polycarboxylic acids and the like) are incompatible with aqueous solutions of salts of organic acids, and these too belong to various chemical and therapeutic classes.
A typical example of a first class of such compounds comprises antihistamines such as: chlorpheniramine, promethazine, azelastine, antazoline, cyproheptadine, tonzylamine, diphenhydramine, emedastine, ketotifen and the like.
A typical example of a second class comprises mucolytics such as: ambroxol, bromexine and the like.
A typical example of a third class comprises vasoconstrictors such as: naphazoline, tetryzoline, tramazoline and the like.
A typical example of a fourth class comprises xcex2-blockers such as: timolol, carteolol and the like.
A typical example of a fifth class comprises antispasmodics such as: ipratropium bromide, octylonium bromide and the like, papaverine, rociverine, toripramide and the like.
A typical example of a sixth class comprises antiseptics such as: chlorhexidine, benzalkonium chloride, benzetonium chloride, benzoxonium chloride, dequalinium chloride and the like.
A typical example of a seventh class comprises antitussives such as: codeine and codeine-like drugs, oxolamine, dimemorfan, cloperastine.
A typical example of an eighth class comprises basic anti-inflammatory drugs such as: benzydamine and the like.
A typical example of a ninth class comprises bronchodilators such as: salbutamol, fenspiride and the like.
A typical example of a tenth class comprises sympathicolytics such as: dapiprazole, prazosin, chlorpromazine and the like.
Further examples of therapeutically useful compounds of a basic nature belong to other classes such as central analgesics, antibiotics, fluoroquinolones and the like.
The compounds of the invention can also contain other traditional types of ingredients such as pH adjusters, antioxidants, stabilizers, preservatives, viscosity enhancers, chelating agents, humectants, colouring matter, substances for achieving isotonia, etc. With regard to isotonia, no macroscopic effects due to the concentration of sodium chloride in the solutions are known.
A person skilled in the art will be able to introduce many variants (such as various salts), without departing from the spirit of the present invention, according to the nature and quantity of the physiologically acceptable compounds used and the type of final composition to be obtained.
For example, the compound having acidic nature and the compound having basic nature may be a polymer such as xanthan gum, carboxymethyl cellulose, chitosan and the like.